package com.atguigu.singleton.type6;

/**
 * @author gcq
 * @Create 2020-09-30
 */
public class SingletonTest06 {
    public static void main(String[] args) {
        System.out.println("双重检查");
        Singleton instance = Singleton.getInstance();
        Singleton instance1 = Singleton.getInstance();
        System.out.println(instance == instance1);
    }
}

// 懒汉式 线程安全 同步方法
class Singleton {
    private static volatile Singleton instance;

    private Singleton() {};

    // 提供一个静态的公有方法，加入双重检查，解决线程安全问题，同时解决懒加载问题
    public static Singleton getInstance() {
        if (instance == null ){
            synchronized (Singleton.class) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }

}